Complex Contact-Based Dynamics of Microsphere Monolayers Revealed by Resonant Attenuation of Surface Acoustic Waves

• Published in: Physical review letters Vol. 116; no. 19; p. 198001
• Main Authors: Hiraiwa, M, Abi Ghanem, M, Wallen, S P, Khanolkar, A, Maznev, A A, Boechler, N
• Format: Journal Article
• Language: English
• Published: United States American Physical Society 13-05-2016
• Subjects: Acoustic attenuation; Contact; Crystals; Dynamical systems; Dynamics; Engineering Sciences; Monolayers; Physics; Vibration; Wave attenuation
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/physrevlett.116.198001

Contact-based vibrations play an essential role in the dynamics of granular materials. Significant insights into vibrational granular dynamics have previously been obtained with reduced-dimensional systems containing macroscale particles. We study contact-based vibrations of a two-dimensional monolayer of micron-sized spheres on a solid substrate that forms a microscale granular crystal. Measurements of the resonant attenuation of laser-generated surface acoustic waves reveal three collective vibrational modes that involve displacements and rotations of the microspheres, as well as interparticle and particle-substrate interactions. To identify the modes, we tune the interparticle stiffness, which shifts the frequency of the horizontal-rotational resonances while leaving the vertical resonance unaffected. From the measured contact resonance frequencies we determine both particle-substrate and interparticle contact stiffnesses and find that the former is an order of magnitude larger than the latter. This study paves the way for investigating complex contact-based dynamics of microscale granular crystals and yields a new approach to studying micro- to nanoscale contact mechanics in multiparticle networks.